Laser Communication Relay Demonstration (LCRD)

OVERVIEW

The Laser Communications Relay Demonstration (LCRD) is the critical next step in preparing laser communications for operational use. A follow-on to NASA’s 2013 Lunar Laser Communications Demonstration mission, LCRD is a technology demonstration to demonstrate and validate the use of optical communications relay satellites. Once operational, this technology could be game-changing for space missions, providing data rates 10 to 100 times better than traditional radio frequency systems.

ESC, at NASA’s Goddard Space Flight Center, developed the LCRD payload, which will travel to space on a "host" spacecraft, the U.S. Air Force’s Space Test Program Satellite-6. This means LCRD is one of multiple payloads on that spacecraft. LCRD will serve as a relay satellite, meaning user spacecraft will pass their data to LCRD, which will then transmit it to receivers on Earth.

LCRD will transmit data to, and receive data from, two dedicated ground stations located in Table Mountain, California, and Haleakala, Hawaii. These ground stations will each house one of the telescopes that will capture the data LCRD sends down and turn them from light back into data. NASA’s Jet Propulsion Laboratory in Pasadena is managing the Table Mountain ground station.

Later in its mission, LCRD will communicate with the Integrated LCRD Low-Earth-Orbit User Modem and Amplifier Terminal (ILLUMA-T) on the International Space Station – this will be the first operational optical communications system for human spaceflight!

TECHNOLOGY

Optical communication is the future of space communications. The technique uses infrared light to transmit digital data to and from spacecraft, providing a much better data rate than current radio-frequency communications systems. This allows newer missions with much higher data collection rates to transmit large amounts of data to the ground more quickly. Optical communications can also be adapted to transmit data at the same rate as RF but be lighter, smaller and require less power than comparable RF systems. These capabilities will have broad applications in the future of human exploration and scientific discovery.

LCRD’s space-based payload was developed at NASA’s Goddard Space Flight Center and will consist of a number of highly sensitive components. Because LCRD is a relay satellite, there will be two sides to the flight payload with an optical terminal on each. That way, one terminal can interface with the user spacecraft and the other can remain directed to ground terminals on Earth. Modems on the payload will translate digital data into laser signals and back again, and the optical module will send those encoded beams of light to the ground or receive them from Earth. The controller electronics will help position the optical modules to the optimum position to receive and transmit data. Because of the two-sided payload, a space switching unit will act as the interface between them, routing data to and from the two optical modules. All of these components will be incorporated into the payload, which will fly on a host spacecraft with other missions.

The Laser Communications Relay Demonstration (LCRD) will fly as a hosted payload aboard a U.S. Air Force spacecraft as part of the Space Test Program (STP-3) mission.Credit: NASA/GSFC Conceptual Image Lab

Radio-frequency communications will also be available for space-to-ground links.

In addition, the LCRD project developed technology for the ground stations that will receive LCRD’s data. These ground stations will each house one of the ground terminals. They will also contain modems to translate encoded light back into data. The ground terminals will be aided by the CODEC, a coding and decoding device designed to restore data that was lost in translation or due to weather conditions, up to a point. This helps to ensure the data received is as complete as possible.

HISTORY

Laser communications truly began with the invention of lasers in the 1960s, which made the technology possible. Over the years, there have been many applications of laser technology, but laser communications is one of the most promising – it can reduce the size, weight and power requirements of communications systems, as well as transmit data at rates orders of magnitude higher than standard radio-frequency systems.

NASA, in partnership with the Massachusetts Institute of Technology Lincoln Laboratory, has made great strides to bring laser communications to space missions in recent years. In 2013, NASA launched the Lunar Laser Communications Demonstration, the first technology demonstration of laser communications, enabling data rates five times faster than ever before from beyond low-Earth orbit. The demonstration was an unqualified success. The Laser Communications Relay Demonstration mission is the next step in verifying the efficacy of the technology.

The Lunar Laser Communications Demonstration (LLCD) made history by using a pulsed laser beam to transmit data over the 239,000 miles between the Moon and Earth at a download rate of 622 megabits per second (mbps) to the terminal in White Sands, New Mexico; its uplink rate was about 20 Mbps.Credit: NASA

OPPORTUNITIES FOR EXPERIMENTERS

NASA’s Laser Communication Relay Demonstration project seeks partners to propose supplemental experiments that help test the functionality of optical communications links. These will be selected via the LCRD experiment proposal process. Proposers of supplemental experiments may be internal or external to the LCRD project, and may include individuals or groups from NASA, other government agencies, academia or industry.

Current communications capabilities between observatories and Earth are often a limiting mission design factor for today’s space-borne science missions, but optical communications can increase scientific return while efficiently using mission resources. LCRD will provide a space-based technology demonstration platform for bidirectional optical communications.

Optical communications will revolutionize space-based science and exploration capabilities by supplying data rates up to 100 times faster than current RF systems. Optical communications can also:

Provide higher data rates than a radio-frequency (RF) system requiring the same mass and power

Require less mass and power than an RF system to provide the same data rate

Eliminate issues such as microwave spectral congestion, spectrum allocation and constrained bandwidth that are commonplace with RF communications

The LCRD investigator team will execute experiments for a minimum of two years, providing high-data-rate optical communications in an operational environment. LCRD experiments will demonstrate that optical communications can both meet NASA’s and other agencies’ growing need for higher data rates and enable lower-power, lower-mass communications systems on spacecraft.

Jet Propulsion Laboratory’s (JPL) Table Mountain Facility, one of the ground terminals that will be used as part of LCRD.Credit: NASA

LCRD’s architecture will enable it to serve as a developmental testbed for advanced communication techniques, including adaptive optics, symbol coding, link layer protocols and network layer protocols. With a dual optical link system, LCRD will serve as the first step in demonstrating optical communications for use in a next-generation space-based relay system and potentially provide early operational support for low Earth orbit (LEO) terminals.

The LCRD architecture consists of:

A payload on a geosynchronous Earth orbit (GEO) satellite—the Space Test Program Satellite-6

Dual optical link system

Optical switch

High-speed RF terminal

Two optical ground stations

An RF ground station

An operations control center

An additional facility for observation and monitoring of LCRD operations and experiments